The present invention relates to compositions for and methods of making polyurethane-based photochromic optical materials and, in particular, to polyurethane-based photochromic optical materials containing polysilsesquioxanes.
Photochromic plastic materials for optical applications have been the subject of considerable attention because of the advantages plastics provide in comparison to glass, including lower density and superior mechanical properties, such as impact strength. Applications for photochromic plastic materials include numerous transparent articles, such as ophthalmic lenses, vehicle or airplane windshields, etc.
Methods of rendering plastic materials photochromic include coating the plastic object with a coating containing a photochromic dye(s), laminating a plastic material containing photochromic dye(s) to the object, casting a photochromic layer onto the object, and incorporation of photochromic dyes directly into the plastic used to form the object. In the case of direct incorporation of the photochromic dye into the plastic that makes up the object, the plastic needs to provide a suitable environment for the photochromic dyes to transform from their light (or faded) state to their darkened state and back with good efficiency. At the same time, the object needs to have certain mechanical properties depending on the object's application.
In the case of ophthalmic lenses used for spectacles, mechanical durability and hardness are required for the various lens-processing steps such as grinding, polishing, edging, and mounting the lens into a variety of frames, such as drill-mount frames. Additionally, for the completed lens, a certain amount of impact strength is required. Generally, the material conditions needed for good photochromic performance (for example, soft and flexible polymers) are different than those required for mechanical processing (for example, hard and rigid polymers). Therefore, compromises are usually made to the material's properties to achieve photochromic performance. One property that can be particularly affected is material brittleness, as one attempts to make a more processable lens. Often chipping and cracking of the lens is encountered during lens deblocking after grinding and polishing, edging, or mounting in frames, particularly of the drill-mount type. Thus it would be desirable to provide a photochromic material that has the physical properties of low brittleness, good impact strength and good photochromic performance typical of a soft, flexible polymer, in combination with the mechanical processability and hardness characteristic of a hard, rigid polymer.